全文获取类型
收费全文 | 2369篇 |
免费 | 221篇 |
国内免费 | 381篇 |
出版年
2024年 | 6篇 |
2023年 | 56篇 |
2022年 | 82篇 |
2021年 | 73篇 |
2020年 | 76篇 |
2019年 | 105篇 |
2018年 | 93篇 |
2017年 | 90篇 |
2016年 | 106篇 |
2015年 | 116篇 |
2014年 | 160篇 |
2013年 | 209篇 |
2012年 | 124篇 |
2011年 | 135篇 |
2010年 | 131篇 |
2009年 | 127篇 |
2008年 | 127篇 |
2007年 | 131篇 |
2006年 | 135篇 |
2005年 | 95篇 |
2004年 | 88篇 |
2003年 | 74篇 |
2002年 | 69篇 |
2001年 | 57篇 |
2000年 | 47篇 |
1999年 | 34篇 |
1998年 | 42篇 |
1997年 | 44篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 25篇 |
1993年 | 21篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 27篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 21篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有2971条查询结果,搜索用时 15 毫秒
131.
132.
The purpose of many microarray studies is to find the association between gene expression and sample characteristics such as treatment type or sample phenotype. There has been a surge of efforts developing different methods for delineating the association. Aside from the high dimensionality of microarray data, one well recognized challenge is the fact that genes could be complicatedly inter-related, thus making many statistical methods inappropriate to use directly on the expression data. Multivariate methods such as principal component analysis (PCA) and clustering are often used as a part of the effort to capture the gene correlation, and the derived components or clusters are used to describe the association between gene expression and sample phenotype. We propose a method for patient population dichotomization using maximally selected test statistics in combination with the PCA method, which shows favorable results. The proposed method is compared with a currently well-recognized method. 相似文献
133.
潜蝇姬小蜂Diglyphus属膜翅目Hymenoptera姬小蜂科Eulophidae,其分布广泛,种类多样,是潜叶蝇的优势寄生性昆虫;潜叶蝇是危害水稻和蔬菜等经济作物的重要害虫。同形潜蝇姬小蜂D.isaea(Walker, 1838)和波氏潜蝇姬小蜂D.poppoea Walker, 1848,安纳潜蝇姬小蜂D.anadolucus Doganlar, 1982,卡布潜蝇姬小蜂D.chabrias(Walker, 1844)的外形相似,需进一步挖掘4种小蜂在形态结构上的种间差异,为其在形态分类及系统发育研究提供更为详细的基础资料。本研究采用非参数检验和多元比例(multivariate ratio analysis, MRA)对40头标本的25个形态特征的测量数据进行分析,研究4种小蜂种间形态差异,筛选出了多个具有分类学意义的特征。非参数检验结果表明,在25个形态特征中,4种小蜂种间差异显著;主成分分析结果发现,前翅(fw.l),后翅(hw.l, hw.w)和体长(b.l)是主成分1和2的代表指标;线性判别分析结果显示b.l∶c.l、hw.w∶ptl.l、hw.w∶mst.l和ppd... 相似文献
134.
采用HPLC测定不同品种淫羊藿黄酮类即淫羊藿苷、朝藿定A、朝藿定B、朝藿定C4种有效成分含量,结合主成分分析对不同品种淫羊藿进行质量分析与评价,并考察淫羊藿对大鼠肾阳虚保护作用.将实验动物随机分为阳虚模型对照组(模型组)、金匮肾气丸干预组(阳性组)、淫羊藿低(125 mg/kg)、中(250 mg/kg)、高(500 ... 相似文献
135.
The Circadian Clock Gene Circuit Controls Protein and Phosphoprotein Rhythms in Arabidopsis thaliana
136.
137.
The medicinal leech Hirudo medicinalis produces various types of proteinase inhibitors: bdellins (inhibitors of trypsin, plasmin, and acrosin), hirustasin (inhibitor of tissue kallikrein, trypsin, -chymotrypsin, and granulocyte cathepsin G), tryptase inhibitor, eglins (inhibitors of -chymotrypsin, subtilisin, and chymasin and the granulocyte proteinases elastase and cathepsin G), inhibitor of factor Xa, hirudin (thrombin inhibitor), inhibitor of carboxypeptidase, and inhibitor of complement component C1s. This review summarizes data on their primary and tertiary structures, action mechanisms, and biological activities. 相似文献
138.
Walenkamp AM Chaka WS Verheul AF Vaishnav VV Cherniak R Coenjaerts FE Hoepelman IM 《FEMS immunology and medical microbiology》1999,26(3-4):309-318
We studied the cytokine profile of peripheral blood mononuclear cells after stimulation with various cryptococcal strains or its purified cell wall components. After 3 h of stimulation, tumor necrosis factor (TNF) alpha levels were strongly increased, whereas interferon (IFN) gamma and interleukin (IL) 10 levels were increased only slightly, or not at all (respectively). In contrast, after 18 h, TNF-alpha and IFN-gamma levels were (strongly) decreased, whereas the IL-10 levels were increased. The IL-1beta, IL-6 and IL-8 levels were equally high throughout the experiment. In order to establish which of the cryptococcal envelope components contributed most to the observed cytokine profile induced by whole cryptococci, glucuronoxylomannan, galactoxylomannan and mannoproteins were purified and partially characterized biochemically. All cryptococcal components elicited a similar cytokine pattern despite the differences in structure. 相似文献
139.
A physiological description of critical velocity 总被引:3,自引:0,他引:3
Hill DW Ferguson CS 《European journal of applied physiology and occupational physiology》1999,79(3):290-293
Although critical velocity (CV) provides a valid index of aerobic function, the physiological significance of CV is not known. Twelve individuals performed exhaustive runs at 95% to 110% of the velocity at which VO2max was attained in an incremental test. VO2max was elicited in each run. Using the time to exhaustion at each velocity, CV was calculated for each participant. Using the time to achieve VO2max at each velocity, which was shorter at higher velocities, a parameter we have designated as CV' was calculated for each participant. During exercise at or below CV', VO2max cannot be elicited. CV (238+/-24 m x min(-1)) and CV' (239+/-25 m x min(-1)) were equal (t = 0.60, p = 0.56) and correlated (r = 0.97, p < 0.01). These results demonstrate that CV is the threshold intensity above which exercise of sufficient duration will lead to attainment of VO2max. 相似文献
140.
Sargent DJ Geibel M Hawkins JA Wilkinson MJ Battey NH Simpson DW 《Annals of botany》2004,94(6):787-796
BACKGROUND AND AIMS: The aims of this investigation were to highlight the qualitative and quantitative diversity apparent between nine diploid Fragaria species and produce interspecific populations segregating for a large number of morphological characters suitable for quantitative trait loci analysis. METHODS: A qualitative comparison of eight described diploid Fragaria species was performed and measurements were taken of 23 morphological traits from 19 accessions including eight described species and one previously undescribed species. A principal components analysis was performed on 14 mathematically unrelated traits from these accessions, which partitioned the species accessions into distinct morphological groups. Interspecific crosses were performed with accessions of species that displayed significant quantitative divergence and, from these, populations that should segregate for a range of quantitative traits were raised. KEY RESULTS: Significant differences between species were observed for all 23 morphological traits quantified and three distinct groups of species accessions were observed after the principal components analysis. Interspecific crosses were performed between these groups, and F2 and backcross populations were raised that should segregate for a range of morphological characters. In addition, the study highlighted a number of distinctive morphological characters in many of the species studied. CONCLUSIONS: Diploid Fragaria species are morphologically diverse, yet remain highly interfertile, making the group an ideal model for the study of the genetic basis of phenotypic differences between species through map-based investigation using quantitative trait loci. The segregating interspecific populations raised will be ideal for such investigations and could also provide insights into the nature and extent of genome evolution within this group. 相似文献